I. Field of the Invention
This invention relates to preservatives used for preserving samples of milk intended for analysis and to methods of preserving such milk samples using preservatives of this type.
II. Description of the Prior Art
Dairy industries or governments in many countries conduct tests of milk output as part of the routine control procedures to ensure high quality, for the calculation of milk payment and for herd improvement. This testing, usually for fat, protein and lactose content, is usually carried out in centralized laboratories and there is often a considerable delay between the sample being taken and the test conducted. In view of this, and in view of the prohibitive cost of refrigerating the samples on a routine basis, it is necessary to preserve the milk with an efficient antimicrobial agent to prevent spoilage. Antimicrobial agents employed for this purpose must not interfere with the test procedure but must preserve the samples for at least 5 days and often up to 10 days.
The preservatives traditionally used for this, namely sodium or potassium dichromate, have come under increasing criticism in recent years owing to their tendency to cause allergic reactions in human skin that comes into frequent contact with the active ingredient. Other substances have been investigated as potential substitutes, and 2-bromo-2-nitropropane-1,3-diol has received considerable attention. When this compound is used in its traditional and well-established antibacterial concentration of 0.02% by weight, it performs efficiently as a sample preservative and does not interfere with the normal testing procedures. The compound is now used extensively in Europe and the U.S.A. for this purpose. One of the drawbacks of using this compound is that, at consistently high temperatures, the product becomes unstable and must be refrigerated to work properly. The use of 2-bromo-2-nitropropane-1,3-diol has therefore not proved to be entirely successful and there is still a need for an improved antimicrobial agent for preserving milk samples.
In U.S. Pat. No. 4,636,476 to Brunt et.al. issued on Jan. 13, 1987, a tablet for preserving milk samples is disclosed. The tablet comprises 2-bromo-2-nitropropane-1,3-diol and a water-soluble solid organic carboxylic acid. The presence of the organic acid is said to stabilize the 2-bromo-2-nitropropane-1,3-diol, thereby providing the tablet with adequate shelf life. However, milk samples preserved with these tablets do not appear to be significantly more stable than when the 2-bromo-2-nitropropane-1,3-diol itself is used.